Artificial tooth making



Oct. 17, 1961 A. F. RYDIN ARTIFICIAL TOOTH MAKING Filed May 2, 1958 nite States This invention relates to artificial teeth and their production and more particularly the invention is concerned with an improved dental technique especially favorable inmaking artificial crowns for pin-teeth and facades for dental bridges and the like but also useful in repairing dentures.

The main object of the invention is to make possible the production of single tooth crowns or tooth facades which look still more lively, natural and Well-matched in the mouth cavity of the patient than most false teeth produced in accordance with earlier dental art and customs. In general this is impossible without far-reaching individual modelling and coloring of each crown or facade and hence it is an object of the invention to facilitate such manipulations and improve the result thereof.

Another object of the invention is to make possible the preparation of an artificial tooth in such a manner that the appearance of those portions of said tooth which may be normally seen from outside the mouth cavity and which are consequently decisive for the natural look of the toothmay be readily established while the patient is still sitting in the dental chair and this by a simple preparatory process carried out by the dentist and including remodelling and coloring a prefabricated blank while repeatedly checking the result in the mouth of the patient. As soon as shape and color of said blank after more or less trial and error has once been found fully appropriate, no changes therein will be necessary during the following process for the completion of the artificial tooth, and consequently the dentist may rest assured that the tooth, when ready, will completely fit the patient at least as far as appearance is concerned. In other words, all the hazards involved in leaving the shaping and coloring of the tooth front or facade to the dental laboratory will be avoided without therefore the dentists Work with the patient in the chair being appreciably increased.

A still other object of the invention is to provide a sort of blank or prefabricated element suitable for forming the front or buccally visible surface of an artificial crown or .tooth facade after appropriate shaping and coloringsuch as by heat-remodelling or grinding or both and subsequent color-painting carried out in a technique somewhat resembling that of water-color painting. Since both remodelling and coloring of such a blank will be rather simple measures for the experienced dentist a far-reaching standardization of such blanks will be possible without affecting the dentists possibilities to produce excellent artificial teeth at a reasonable cost.

Furthermore the invention has for its object to make possible the production of improved wear-resistant crowns having a surface layer of hard material and a body of softer material forming a somewhat elastic cushion therebeneath.

With these and other objects in view the invention will now be described and illustrated by way of example, reference being had in the following description to the appended drawing wherein:

FIG. 1 is a front elevation of a prefabricated blank for an upper incisor front,

FIG. 2 is a side view of the same blank.

FIG. .3 is a cross section taken along line 3-3 in FIG. 1,

FIG. 4 is a front elevation of a similar prefabricated blank for an upper cuspid front,

FIG. 5 is a side view of the blank shown in FIG. 4,

3,fi0d,34-3 Patented Get.- 17, 1961 "ice FIG. 6 is a front view similar to FIG. 1 and illustrating the remodelling of a blank as a first step in the preparation of an artificial tooth front or facade,

FIG. 7 is a selectional elevation of a remodelled blank illustrating the painting or coloring of the back of said blank as a second step in the preparation of a tooth facade,

FIG. 8 is a sectional elevation similar to FIG. 7 and showing a protective coating applied to the painted back of the blank as a discretionary measure to avoid color changing of the blank during the following manipulation thereof,

FIG. 9 is a longitudinal section of a complete pin-tooth built up with a front blank as in FIGS. 1-3,

FIG. 10 is a similar section of an artificial facade on a vital tooth,

FIG. 11 shows a longitudinal section of a complete pin tooth for a lower jaw which has been built up by starting from a shell blank similar to that of FIG. 1 but made of porcelain or like wear-resistant, hard material instead of thermoplastic resin, and

FIG. 12 is a similar section of a premolar with a crown including a porcelain shell blank, this latter figure having for its purpose to show the lingual extension of a blank used for a posterior tooth particularly in the lower jaw.

As a first step in carrying out the invention a blank or preliminary element is provided. Such a blank may be made of thermoplastic resins, e.g. acrylic resins, this being preferred particularly for blanks intended for teeth in the upper jaw-or by any suitable, harder and more wear-resistant material such as porcelain or certain types of glasssuch materials being preferred particularly for blanks to be used in teeth of the lower jaw. In either case the blank is preferably factory-made in series of stand ardized sizes and shapes, so that suitable blanks for different types of crowns, such as incisors and cuspids, are available.

As will be seen from FIGS. 15 each blank comprises a thin-walled shell 10 or 11 respectively generally resembling a small scoop or spoon and having preferably a handle 12 projecting from its thickened incisal or cusp portion as shown. If the blank is press-molded of a.

thermoplastic resin, the handle 12 may form an integral part thereof, or otherwise the handle may be attached in any suitable manner such as by cement or the like. The handle may also be dispensed with, particularly in blanks to be used in the lower jaw, which may commonly be easily handled by tweezers or like tools. The handle, if any, may have a hole 13 to be threaded on to a wire ring or like holder (not shown) for keeping the blanks properly assorted.

The spoonor scoop-like shell 10 or 11 has a rather small thickness increasing more or less uniformly from the cervical edge portion A towards the incisal or cusp portion B. About midway therebetween, i.e. in the cross section shown in FIG. 3 for example, the wall thickness of the shell is about 1 millimeter (.04 in.). Consequently it will be understood that the thickness of the shell 10 or 11 is of substantially the same order as the thickness of the enamel layerof a natural tooth, and the shell is also intended to form only the external layer of an artificial crown or facade, as will appear from the following. a a

In spite of its small thickness the artificial enamel shell 10 .or 11 is self-supporting and form-persistent at normal temperatures so that it may be readily produced and, handled as a separate element or article. Furtherdistributed in the resin but instead caused to form flocks therein, so that the shell will be neither fully transparent nor completely opaque.

The enamel shell blank is formed to cover the buccally visible front and incisal or buccal cusp portions of the artificial tooth to be made and the sides of the scooplike shell will then cover the approximal surfaces of such tooth, which are buccally visible. It will be readily appreciated that each enamel shell or 11, at least if made of thermoplastic resins, may easily be remodelled by heating and bending or squeezing, and furthermore by grinding and cutting, and consequently the original form of the shell or blank is not particularly critical. In practice it has been found adequate to determine the depth and width of the opening between the adjacent teeth to be filled by the new crown or facade and to remember the general type of tooth to be made when selecting a suitable blank. Then the blank is likely to fit well after a suitable and simple remodelling process mainly concentrated on adapting the cervical edge of the scoop-like shell to the prepared root or a corresponding gingival portion of a bridge. FIG. 6 is intended to illustrate such an adaptation of a shell blank 10 as shown in FIG. 1.

Remodelling the prefabricated enamel shell is generally considered to be the first step in the preparation of an artificial tooth crown or facade according to the invention. Another step, commonly but not necessarily subsequent to the remodelling, is the coloring or painting of the back of the shell. Such painting is illustrated in FIG. 7 and has for its purpose to give the desired shade and luster to .the artificial enamel shell before the body of the crown or facade is built up. This is important, because it gives the dentist a possibility he never dreamed of before to take the shading and matching of the artificial tooth in his own hands, thus avoiding all hazards involved in leaving that delicate work to the laboratory.

It will be fully appreciated that the result obtained by remodelling and painting of the shell may be easily checked directly in the mouth of the patient and repeated corrections may be made until the most excellent matching is secured. It is preferred to use opaque colors for the painting and to apply them in a sort of water color painting technique, the colors being composed on a base kindred or at least well adhering to the material of the shell. For an acrylic shell the color may be made by thoroughly mixing a considerable proportion of suitable pigments to a mixture of monomer and polymer acrylic resin and causing said complete mixture to harden ,to a

cake. Then the cake is .superficially dissolved by resin monomer, chloroform or like solvent applied by means of a brush or other implement used for transferring the color to the enamel shell.

It should be mentioned that painting the shell is no intricate process. In most cases it is sufiicient to apply one and the same color over the entire back of the shell, since different incisal, body and cervical shades are automatically obtained by the different thicknesses of the shell at these areas. Still it should be remembered that only .the back of the shell is painted and thus the color will be seen (and checked) through the translucent shell with its refractive and reflective properties, and since the shell is curved and mostly has a somewhat undulated surface like .a natural enamel layer, the color will look lively and varying in spite of its uniformity. If desired, however, there is nothing preventing the dentist from applying local stains of brighter or darker color or from making scratches or the like giving the impression of imperfections in the tooth.

When the color of the painted shell is checked for the first time in the mouth of the patient, it may be advisable though not always necessary to place a piece of paper or the like behind the shell to form an apaque back-ground. This is simply done to prevent the darkness of the mouth cavity from dulling the color of the shell should the color film applied thereto not be .dense. For similar reasons,

a layer of dense white or slightly shadedrcolor may be applied on the painted back of the shell as a last precautionary step in the coloring process.

Now, with its form and color completely matched, the scoop-like shell is ready for further'manipulation, i.e. to be combined with a suitable body portion and united to a backing such as a post or bridge construction, but before this a protective coating 14 is usually applied to the painted back of the shell 10 as shown in FIG. .8 to protect the thin color film 15 during the following manipulation of the shell. Such coating is accomplished by spreading a relatively thin layer of cement, preferably a cold-hardening plastic resin composition in a paste-like state over the painted back of the shell. This protective coating 14 will then unite with the body portion subsequently formed of a similar material as will be described in the following.

A number of ready-made crowns including a shell as above described have 'been shown in FIGS. 9-12 inclusive. In FIG. 9 a thermoplastic resin shell l0-remodelled and painted as described with reference to FIGS. 6 and 7is combined with a thermoplastic resin body 16 to form a pin-tooth crown on a pin-post 17 with a root cap 18 and back reinforcement 19 all of gold or other suitable metal. The resin used in the body 16 is preferably an acrylic resin with enough pigment added to give it an opaque dentin-like appearance. If desired, a coldhardening acrylic resin composition, i.e. a mixture of acrylic monomer, acrylic'polymer and suitable catalysts and accelerators to let the mixture polymerize and harden rather rapidly without the application of heat and pressure, may be used for the body so .that no special mold will be necessary for processing. It will be readily understood that the shell handle 12 is removed as soon as it is not longer needed and the incisal edge or cusp is then ground and polished.

A similar technique has been employed to combine the shell 11 of FIG. 10 with a resin body 20 to a facade on a vital tooth, which has been prepared and provided with a gold jacket 21'.

It should be particularly noticed in FIG. 9 that the cervical edge portion A of the shell 10 is allowed to extend all up over the 'buccal side of the prepared root 22 to the bottom of the gum pocket. This has been found particularly advantageous because it invites the gum to grow partly down over the front surface of the shell to restore a natural gum contour. Consequently the shell 10 is always chosen a little longer than the actual height of the crown.

In FIGS. 11 and 12 the crowns have been built up starting from a shell blank 23 and 24 respectively made of porcelain, glass or other hard but usually also brittle material. The most prominent advantage of such materials in the preparation of artificial teeth is their great resistance to wear in comparison with the softer thermoplastic resins nowadays most commonly used in dentistry. Their drawback, however, is their brittleness, but this drawback is overcome when the materials are used in accordance with the present invention. Generally speaking, the shell made of such materials is prepared in substantially the same manner as hereinbefore described with reference to the shells of thermoplastic resin with the exception that the remodelling process can of course not go so far and must be mainly based on grinding.

Contrary to a resin shell, a porcelain or glass shell is always chosen a little shorter than the total height of the crown to be made and the crown body 25 and 26 respectively is always built up by a thermoplastic resin capable to form a somewhat elastic cushion all between the brittle shell 23, 24 and its related pin-post 27 or 28 with its integral root cap 27' and 28 respectively. It is important that the body material completely separates the brittle shell from the post and particular attention should be paid to expose the body material between the cervical edge of 5 the shell and the root caps as indicated at 29 in both FIG. 11 and FIG. 12.

From the foregoing description of certain specific applications of the invention it will be readily understood that the novel technique in making artificial crowns and facades affords considerable advantages over the prior art particularly as far as shading and color matching of the tooth front is concerned. The use of prefabricated thin shell blanks also eliminates the delicate trimming of a wax model and gives a maximum freedom in designing the backing structure. Furthermore it willbe understood that certain changes and modifications in the applications shown and described may be resorted to in order to meet practical demands.

I claim:

1. A method of making an artificial tooth comprising the steps of providing a separate element of thermoplastic, translucent synthetic resin material in the form of a shovel-like, hollow shell blank with a concave back and having substantially the same thickness and extension as the enamel layer of the buccally visible portions, including the tip, of the natural tooth to be reproduced, trimming said shell blank and heating and deforming it to a desired shape so as to match the contours of the tooth to be replaced, subsequently applying a coating of paint having a base which is chemically related to the material of the blank to the concave back of said translucent blank to let the color of said paint appear through the material of the shell blank, and finally combining said prepared shell blank with a body forming mass filling out said hollow shell and uniting it to a backing.

2. A method as in claim 1, wherein a protective coating of opaque, hardening synthetic resin material chemically related to the material of the shell blank is applied on the painted back of the shell blank before the latter is combined with the body forming mass and united I to the backing.

2,219,058 Streim Oct. 22, 1940 2,514,075 Kelly July 4, 1950 2,700,184 Levine Jan. 25, 1955 2,700,822 Infante Feb. '1, 1955 

